The overall goal of this project is to gain a better understanding of one aspect our innate antimicrobic defenses, namely that involving the macrophage. While the contributions to mammalian defense by antibody and lymphocytes are well-recognized, the activity of our constitutive defense, in the absence of antigen- directed events, is less understood. The antibacterial effects of macrophages are particularly significant in individuals manifesting inadequate specific immunity due to age (e.g., neonates), genetics (e.g., inherited immunodeficiency), or infection (e.g., acquired immunodeficiency,). Our approach will be to examine the ability of macrophages to recognize selected pathogenic bacterial in in vitro binding assays. These studies will provide information on microbial recognition by macrophages as well as a monitoring system for subsequent studies. The second part of this study involves a characterization of the lectin-like receptor on the intact macrophage through use of proteases and cellular modulating agents and by blocking studies with various glycoconjugates. The third specific goal of this study is to purify the bacterial binding receptor from the macrophage membrane and assess its ability to bind to bacteria. Antibody to the receptor will be tested for its ability to block bacterial binding. A long-term objective of this study is to determine whether bacterial-binding receptors on mammalian macrophages represent an evolutionarily conserved defense mechanism.